This invention relates to prostaglandin I.sub.2 derivatives.
Prostaglandin I.sub.2 (PGI.sub.2, prostacyclin) is a compound discovered in 1976 by J. R. Vane et al., which has called attention as a substance exerting potent platelet aggregation-inhibiting and aorta-contracting activities after having been biosynthesized from archidonic acid via an endo-peroxide (PGH.sub.2) at the aortic wall [CdEN, Dec. 20, 1976, p. 17; S. Moncada, R. Gryglewski, S. Bunting and J. R. Vane, Nature, 263, 633 (1976)]. ##STR1##
However, PGI.sub.2 which has an exo-enol structure is extremely unstable even in neutral aqueous solution and is readily subjected to conversion to 6-oxo PGF.sub.1 which has almost no physiological activities. Such instability of PGI.sub.2 is a big obstacle to its use as a drug. PGI.sub.2 is also metabolized quickly in the body and its physiological actions are not durable.
It is an object of this invention to overcome the disadvantages inherent in PGI.sub.2.
Another object of this invention is to provide novel PGI.sub.2 derivatives which are stable and possess platelet aggregation-inhibiting, hypotensive anti-ulcer and other activities.
Other objects and advantages of this invention will be apparent from the descriptions hereinbelow.